This invention relates to septa which are widely used in the chemical, medical, and biochemical industries.
Septa are piercable, mechanical barriers typically positioned between a vessel and its contents (usually a liquid) and the vessel""s ambient environment. In such a configuration a septum prevents contamination of the vessel contents or contamination of the environment by the vessel contents. A conventional septum 20 is illustrated in FIG. 1. Access to a vessel 10 is gained by piercing septum 20 in an axial direction 40 with a small gauge tubing such as a hypodermic needle 30 on a syringe 34, which may then used to transfer liquid or other material into or out of vessel 20. A typical septum 20 is comprised of rubber or other elastomeric material, pressed or otherwise inserted into a rigid collar, such as a vessel neck or cap so as to hold the elastomer under radial compression (direction 44 in FIG. 1). When pierced by a small gauge tube, the compressed elastomer creates a seal around the tube with a radial reaction force. When the tube is withdrawn, the compressed elastomer forces the hole closed, thus, resealing the vessel.
To function as described above, the septum must be able to contain compressive forces in the axial direction during tubing penetration and withdrawal. This is conventionally done by making the dimension of the septum in the axial direction (the septum xe2x80x9cthicknessxe2x80x9d) deep enough to resist the compressive forces at the septum center. To improve the sealing capabilities, sometimes a very soft elastomer is sandwiched between two or more elastomers which are more rigid than the soft elastomer. The rigid elastomers create the axial resistance needed to maintain reasonable compressive forces in the soft elastomer during tube penetration and following withdrawal.
There are two major drawbacks of the above described plug type septa. First, the septum must have sufficient axial depth to maintain compression in the center of the plug during tube penetration and withdrawal. This makes space-critical applications difficult. Second, coring may occur during septum penetration. That is, during axial penetration the septum elastomer resists with an opposing axial reaction force causing a xe2x80x9ccookie cutterxe2x80x9d effect at the interface between the end of the tube wall and the septum elastomer. This can cut a small core from the material, possibly plugging the tube.
It would be desirable then to provide a septum which could be relatively thin, resists coring, and is simple to fabricate.
The present invention then, provides septum penetrable by a member and which maintains a seal following member penetration in an axial direction and withdrawal. The septum includes a first layer of resilient material having first and second opposed surfaces. A second layer extends across the first surface of the first layer and is in radial tension. The septum may also include a third layer which extends across the second surface of the first layer, which third layer is in radial tension.
The second and third layers are continuous and may be under any suitable radial tension, for example between 5 and 1000 newton/m, and optionally between 10 to 100 newton/m, or between 20 to 80 newton/m, A resilient material, such as a suitable polymer, may be used for any of the first, second, and third layers. Each of the layers may have any suitable thickness which will allow axial penetration of the member while maintaining a seal following penetration and member withdrawal. For example, each layer may have a thickness of less than 10 mm or 1 mm, such as between 0.01 to 10 mm, 0.02 mm to 2 mm, or 0.05 mm to 1 mm. The first layer may be held in compression by the second and third layers, with a force for example of between 5 and 1000 newton/m, and optionally between 10 to 100 newton/m, or between 20 to 80 newton/m. The foregoing tension and compression forces are radial forces as measured at the edge of the layers.
The present invention also provides a septum assembly which includes any rigid periphery which defines an opening, for example an opening into any chamber such as that of a vessel or conduit. The opening may support a septum of any type of the present invention. Optionally, the septum may be fastened to the periphery of such an opening. The opening in such an assembly may, for example, have an area of between 0.001 cm2 to 100 cm2, or 0.01 cm2 to 50 cm2, or even 2 cm2 to 30 cm2 or to 20 cm2.
The present invention further provides a method of fabricating a septum such as a septum of the present invention. Such a method may include applying radial tension to the second layer (and third layer, when present) and bonding the second layer to the first layer of resilient material such that the bonded second layer (and third layer, when present) is under tension. The tension can be applied either prior to or after bonding. For example, the tension may be applied prior to and during bonding to the first layer. One way for providing tension in this situation is by pulling on the layers. Alternatively, the tension may be applied after the bonding of the layers. For example, by means of chemical or thermal shrinkage.
Different embodiments of septa and methods and devices of the present invention can provide any or more of a number of useful features. For example, the septa may be made thin while still maintaining the sealing following axial tube penetration and withdrawal. Further, septa of the present invention can resist coring , be simple to fabricate, and require only a low force for member penetration.